The Cold Spot as a Large Void: Lensing Effect on CMB Two and Three Point Correlation Functions

Abstract

The "Cold Spot" in the CMB sky could be due to the presence of an anomalous huge spherical underdense region - a "Void" - of a few hundreds Mpc/h radius. Such a structure would have an impact on the CMB two-point (power spectrum) and three-point (bispectrum) correlation functions not only at low-l, but also at high-l through Lensing, which is a unique signature of a Void. Modeling such an underdensity with an LTB metric, we show that for the power spectrum the effect should be visible already in the WMAP data only if the Void radius is at least L \gtrsim 1 Gpc/h, while it will be visible by the Planck satellite if L \gtrsim 500 Mpc/h. We also speculate that this could be linked to the high-l detection of an hemispherical power asymmetry in the sky. Moreover, there should be non-zero correlations in the non-diagonal two-point function. For the bispectrum, the effect becomes important for squeezed triangles with two very high l's: this signal can be detected by Planck if the Void radius is at least L \gtrsim 300 Mpc/h, while higher resolution experiments should be able to probe the entire parameter space. We have also estimated the contamination of the primordial non-Gaussianity f_NL due to this signal, which turns out to be negligible.

v1: 18 pages, 12 figures; v2: 19 pages, 12 figures, calculation of bispectrum improved, reference added, published version; v3: 19 pages, 12 figures, refined eq.(9) and related figures, conclusions strengthened

References in corpus (9)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results
• Hemispherical power asymmetry in the three-year Wilkinson Microwave Anisotropy Probe sky maps
• Increasing evidence for hemispherical power asymmetry in the five-year WMAP data
• The non-Gaussian Cold Spot in the 3-year WMAP data
• Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies I
• Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies: The Effect of a Cosmological Constant
• Needlet Detection of Features in WMAP CMB Sky and the Impact on Anisotropies and Hemispherical Asymmetries
• Impact of Secondary non-Gaussianities on the Search for Primordial Non-Gaussianity with CMB Maps
• The Cold Spot as a Large Void: Rees-Sciama effect on CMB Power Spectrum and Bispectrum

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• Non-Gaussian Signatures in the five-year WMAP data as identified with isotropic scaling indices
• The effects of structure anisotropy on lensing observables in an exact general relativistic setting for precision cosmology
• CMB seen through random Swiss Cheese
• On the origin of the Cold Spot
• 21-cm Lensing and the Cold Spot in the Cosmic Microwave Background
• Two-point Correlation Functions in Inhomogeneous and Anisotropic Cosmologies
• Analysis of $\sim 10^6$ spiral galaxies from four telescopes shows large-scale patterns of asymmetry in galaxy spin directions
• How Sensitive is the CMB to a Single Lens?
• Detecting the Cold Spot as a Void with the Non-Diagonal Two-Point Function
• The CMB cold spot under the lens: ruling out a supervoid interpretation
• CMB Lensing and Giant Rings
• Search for non-Gaussianities in the WMAP data with the Scaling Index Method
• Using CMB polarization to constrain the anomalous nature of the Cold Spot with an incomplete sky-coverage
• The CMB Cold Spot under the lens II: Lensing signatures in polarization and cosmic texture footprints